CPM Seminar
Dissipation in Micro/Nanomechanical Resonators
Srikar Vengallatore
Department of Mechanical Engineering McGill
University
Micro/nanomechanical resonators are the building blocks of entirely new
classes of systems for sensing (force-detected magnetic resonance imaging;
mass spectroscopy; probe microscopy; medical diagnostics), ultra-low power
signal processing, vibration energy harvesting, and fundamental studies
at the intriguing boundary between classical and quantum physics. All
these applications share one essential requirement: minimize dissipation by
structural damping and increase the quality factor (Q) of resonance. In
this talk, I will describe our efforts to probe the mechanisms of dissipation
in micro/nanomechanical resonators. The first part will focus on progress
towards the long-standing goal of predictive modeling and rational design
of damping. Under certain conditions, and for a small and special class of
materials, it is possible to machine microresonators that can vibrate with
very low dissipation approaching the ultimate thermodynamically-mandated
limits of damping. This limit is set by the mechanism of thermoelastic
damping. Models for thermoelastic damping and experiments with single-crystal
silicon microresonators will be presented.
The second part of the seminar will focus on dissipation in ultrathin
nanocrystalline films of common metals. These materials are widely used
as coatings on micro/nanomechanical resonators to enhance electrical
conductivity, optical reflectivity, and surface chemistry. Unfortunately,
they also degrade the performance by causing a disproportionate increase
in dissipation. In these films, damping is dominated by internal friction
caused by the irreversible motion of crystallographic defects. As a first
step towards scale-dependent process-structure-dissipation correlations,
we have measured the effects of frequency, thickness, and grain size on
internal friction in nanocrystalline aluminum films. The details of these
measurements, and the contribution of grain-boundary sliding to internal
friction in aluminum films, will be discussed.
Thursday, January 12th 2012, 15:30
Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103)
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